Boron toxicity in Cannabis: Images and Info

After having a couple of discussions with a couple of ICmag'ers, I thought I would post a thread for a nutrient toxicity none of us had ever seen in cannabis: boron.

Below is my current nutrient test mix, I messed up in finding ppm of B from boric acid. When converting to decimal from percent I converted 17.48% to 0.01748. So, I recently used 7.09 ppm B, but I was trying to use ~0.86 ppm B. Boric acid, when mixed with water, provides B that is immediately available to the plants.

I should have used 0.015 g (15 mg) of boric acid per gallon, for a total of ~0.86 ppm, not 0.15 g (150 mg) of boric acid per gallon for a total of ~7.09 ppm.

The soilless solution pH is ~6.0-6.15 and EC was ~0.98 using PourThru method from North Carolina State University. The pH and EC readings accounted for water temperature.There are two expressions of B toxicity in plants: (1) yellowing and burn of leaf tips and edges in older leafs; and (2) die back of young leafs and meristem(s). The former is for plants were B is immobile and latter is for plants where B is mobile.

I am pretty sure B is immobile in cannabis, as it is for most species. For species where B is mobile, the plant produces polypols[1] and moves complex sugars (ex., sorbitol) through phloem[2]. I spent the past little while trying to find if cannabis produces polypols and moves complex sugars; I haven't found anything yet. If anyone has any info I would love to read up.

At this point I think B is immobile in cannabis, esp. because of the classic B-immobile toxicity symptoms my plants are showing. The only other thing it could be is my use of yucca extract, which has never done this, but I did use 3.5 ml/gal instead of 2.5 ml/gal.

Boron toxicity in plants not considered boron-tolerant often begins about 2 ppm. About 0.5-1 ppm B is a good goal for fertigation.

Boron is an anion, which means it is easily flushed from soilless solution. If the media has low AEC (anion exchange capacity), for example, due to lack of certain clays particles and powders, humus, etc.


Pics:


Toxicity symptoms for B-mobile plant (Ligustrum) and B-immobile plant (Strawberry):Concentration by ppm of B at various areas of leaf, for B-mobile Plant (Apple) and B-immobile plant (Walnut):Toxicity symptoms in alfalfa, a B-immobile plant:





Toxicity symptoms in pistachio, a B-immobile plant:
Deficiency symptoms in tomato, a B-immobile plant (by ppm):

Leafs from my plants after 7 ppm B, it starts at older-middle leaves, not at very top and not at very bottom (pics aren't the greatest, they are from my camera phone):














References:

Thanks Spurr. Your little decimal point problem proved to be quite the interesting learning experience.

I find myself quite curious about micro nute levels. I am curious if the goal should be to merely supply enough to avoid deficiencies or if there is an advantage to playing around with amounts between deficient and toxic

Obviously the experiments need to be very well designed when mere 6 ppm errors make that much difference.

YosemiteSam said:

Thanks Spurr. Your little decimal point problem proved to be quite the interesting learning experience.

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No doubt. Good thing I've been growing long enough to realize my plants should be okay in a little bit, esp. new growth. So no need to stress over spilled milk.

YosemiteSam said:

I find myself quite curious about micro nute levels. I am curious if the goal should be to merely supply enough to avoid deficiencies or if there is an advantage to playing around with amounts between deficient and toxic

Click to expand...

I think shooting for sufficient range is the best goal; but I haven't tested 'large' amounts of micros before.

YosemiteSam said:

Obviously the experiments need to be very well designed when mere 6 ppm errors make that much difference.

Click to expand...

IMO such experiments need to be done with water culture, in net pots, so one can control very precisely the ppms given to the plant (via very frequent rez changes). I have a pretty good paper on this topic, and why using hydro (without substrate) is the best option.

I have been planing on recording (along with images) element deficiency and toxicity, for cannabis, from N all the way to Ni. I plan to use water culture and fertigation water (fertilizer) testing from rez to see what the plant is taking up and or converting, etc.

when i saw what i thought was boron toxicity it looked exactly like the strawberry pic, except the rust happened mid leaf, not on the tips.

curious to see more.

Very helpful and thanks for a week’s worth (or more) of interesting reading.

very interesting. thanks for sharing.

Thanks from me also spurr

Please keep up the excellent work brother!

so you would have a side by side plants right now??? any pics of that...then this would be even more intresting...

desertsquirrel said:

when i saw what i thought was boron toxicity it looked exactly like the strawberry pic, except the rust happened mid leaf, not on the tips.

curious to see more.

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By "mid leaf" do you mean along the middle of each leaf blade?

I am seeing the toxicity start at leaf tips, then move downward along the leaf edges to toward the petiole.

The strawberry pic was a very advanced stage of toxicity, and they used 25 ppm B, I only used 7 ppm B. Some of my weaker plants (i.e., poor seed strains of the cultivar GrapeGod, from Next Generation Seed Co.) look worse, more akin to the strawberry pic, than my healthier and more robust seed strains of GrapeGod.

I could take a few whole plant pics today, of the strains of GrapeGod with the worst toxicity, if you want to see more.

FWIW, I flushed them for the past two days with ~2.5 gallons RO water per each pot. I have ~18 pots, each is a 5 gal "Plant Warrior" (new type of air-pruning pot) which really holds ~4 gallon so media. After flushing for two days all the plants are looking better and seem to be recovering.

SOTF420 said:

Thanks from me also spurr

Please keep up the excellent work brother!

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No worries, and thanks, I will try.

Core said:

so you would have a side by side plants right now??? any pics of that...then this would be even more intresting...

Click to expand...

I could post a couple of side-by-sides, but all plants got 7 ppm B, so they all are exhibiting toxicity. Granted, some more than others. I could take a side-by-side of plants with light toxicity vs heavy toxicity symptoms ... but I'm not sure how helpful that would be.

wow. thanks again Spurr, another informative post...

i'll be interesed in some of the other nutrient def/toxicity results, particularly Aluminum.
i'll just park it here and surveil.

peace,
tr

trichrider said:

wow. thanks again Spurr, another informative post...

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No worries, glad to help, it's learning experience for me too

trichrider said:

i'll be interesed in some of the other nutrient def/toxicity results, particularly Aluminum.
i'll just park it here and surveil.

Click to expand...

You may have to wait awhile, I don't have plans to carry out the deficiency and toxicity testing for at least two months.

More pics as requested:

hello Spurr thanks for dropping them plants mate....a overall picture just say's more about a plant...whats realy weird that is is very similar to a magnesium dissorder
but i noticed a small diffrence in color on ya pics...decaying parts seem more redish at some points...
Nway the burnt tips always is a indicator you are over the line

Sorry to bump a super old thread but this is of interest and quite contrary to the information provided here.

https://www.cannabisbusinesstimes.c...-fertilization-nutrition-deficiency-toxicity/

The claim is they tested boron and concluded/estimated cannabis can actually use 8-10ppm. This is from North Carolina State University, hard for me to imagine they are making mistakes such as publishing a 10-25x figure for B levels.

We know you found boron toxicity in your test but that doesn’t mean cannabis can’t use a lot more boron right unless there is some decimal point errors in their numbers. What if you added the other necessary elements that boron needs in order to use the additional boron? Supposedly you need additional N K and Ca before you can process the any additional boron.

Does that article change any opinions? Toxicity described by them is exactly as you describe and show so that’s established, but can we push our girls and produce larger plants and flowers by adjusting ratios to work with additional B? I bet. Anyone care to dive in on a 10 year old thread about B?

By "mid leaf" do you mean along the middle of each leaf blade?

Click to expand...

I am seeing the toxicity start at leaf tips, then move downward along the leaf edges to toward the petiole.

The strawberry pic was a very advanced stage of toxicity, and they used 25 ppm B, I only used 7 ppm B.

Some of my weaker plants (i.e., poor seed strains of the cultivar GrapeGod, from Next Generation Seed Co.) look worse, more akin to the strawberry pic, than my healthier and more robust seed strains of GrapeGod.

I could take a few whole plant pics today, of the strains of GrapeGod with the worst toxicity, if you want to see more.

FWIW, I flushed them for the past two days with ~2.5 gallons RO water per each pot.

I have ~18 pots, each is a 5 gal "Plant Warrior" (new type of air-pruning pot) which really holds ~4 gallon so media.

After flushing for two days all the plants are looking better and seem to be recovering.
___________________________________
custom bottled water

George said:

Sorry to bump a super old thread but this is of interest and quite contrary to the information provided here.

https://www.cannabisbusinesstimes.co...ency-toxicity/

The claim is they tested boron and concluded/estimated cannabis can actually use 8-10ppm. This is from North Carolina State University, hard for me to imagine they are making mistakes such as publishing a 10-25x figure for B levels.

We know you found boron toxicity in your test but that doesn’t mean cannabis can’t use a lot more boron right unless there is some decimal point errors in their numbers. What if you added the other necessary elements that boron needs in order to use the additional boron? Supposedly you need additional N K and Ca before you can process the any additional boron.

Does that article change any opinions? Toxicity described by them is exactly as you describe and show so that’s established, but can we push our girls and produce larger plants and flowers by adjusting ratios to work with additional B? I bet. Anyone care to dive in on a 10 year old thread about B?

Click to expand...

my main plot, 1000 sq feet, tested 3.2ppm B this spring, I was shooting for 7ppm B when I balanced the minerals need to send in a post harvest sample and see where it ended up.



I added 2.25#s of borax.
tried to raise Sulfur to 1000ppms to match K and P and added a shit ton of mn to get close to my Fe numbers. lots of copper and zinc too. my Calcium was at 81% and I bumped it to 85% per Slownickle.

quality is way up this year in terms of terps, flavor, and effects. growth was faster, less fungal and pest pressure. kind of shocked at how close it got to indoor quality and in some strains the quality was better than ins, Gelato and 91/SKVA crushed the gas over the ins.

picture quality it looks about the same as previous years but the mineral balancing was a massive improvement to quality. #ThanksSlow!





Josh D OGK



Chaco's Gift




Forum GSC, this never got the flavor quality of the ins before but this year it's way dank!


my fungal is crushing too!


as above, so below...

Chunkypigs said:

my main plot, 1000 sq feet, tested 3.2ppm B this spring, I was shooting for 7ppm B when I balanced the minerals need to send in a post harvest sample and see where it ended up.



I added 2.25#s of borax.
tried to raise Sulfur to 1000ppms to match K and P and added a shit ton of mn to get close to my Fe numbers. lots of copper and zinc too. my Calcium was at 81% and I bumped it to 85% per Slownickle.

quality is way up this year in terms of terps, flavor, and effects. growth was faster, less fungal and pest pressure. kind of shocked at how close it got to indoor quality and in some strains the quality was better than ins, Gelato and 91/SKVA crushed the gas over the ins.

picture quality it looks about the same as previous years but the mineral balancing was a massive improvement to quality. #ThanksSlow!





Josh D OGK



Chaco's Gift




Forum GSC, this never got the flavor quality of the ins before but this year it's way dank!


my fungal is crushing too!


as above, so below...

Click to expand...

Damn i never come back to anything.

WOW great post dude!! That is exactly what i was hoping to see. Im encouraged to experiment with micros heavily now being that youre confirming the beliefs of how to work those ratios of micros and Ca/P/K to try and maximize growth and quality. I noticed when i added P without Ca i got huge stems but they were hollow stems. P is no good without Ca obviously and the system needs the boron to match. That was what really got me going when i saw the links. Its funny to see how deep the rabbit hole is.